I personally feel Mining is another OP game mechanic that needs to be tapered down.
Trade rank was always a pointless Elite Rank because of various fast cash exploits or META play over the years. Credits in ED are pointless now and stupid easy to make, given that trade and credit earning were always at the core of Elite as a 'game' i find it sad that ED has ultimately developed this way.
Mining is just the latest Conda in a day mechanic. Separating it from Trade just slows down a players ability to reach trade Elite rank but does not really address the main issue as far as im concerned which is that Mining is over powered.
A new mining rank adds no value to Elite, its just another grind (if ranked by tonnage and not credits as suggested above) towards a pointless thing.
You gave me an idea. What if you got some kind of bonus for specializing in 1 career? Its like multi-classing in DnD, you can do it for the extra spells, but you'll never get that 4th attack for your 20th level Fighter unless you remain a fighter.